On-Demand Dynamic Receive Queue Resizing

This commit causes the receive queue to dynamically
resize to fit incoming messages.

Fixes #557

include/websock.js

@@ -66,12 +66,13 @@ function Websock() {
 
 (function () {
     "use strict";
-
     // this has performance issues in some versions Chromium, and
     // doesn't gain a tremendous amount of performance increase in Firefox
     // at the moment.  It may be valuable to turn it on in the future.
     var ENABLE_COPYWITHIN = false;
 
+    var MAX_RQ_GROW_SIZE = 40 * 1024 * 1024;  // 40 MiB
+
     var typedArrayToString = (function () {
         // This is only for PhantomJS, which doesn't like apply-ing
         // with Typed Arrays
@@ -345,9 +346,49 @@ function Websock() {
             return new Uint8Array(this._sQ.buffer, 0, this._sQlen);
         },
 
+        _expand_compact_rQ: function (min_fit) {
+            var resizeNeeded = min_fit || this._rQlen - this._rQi > this._rQbufferSize / 2;
+            if (resizeNeeded) {
+                if (!min_fit) {
+                    // just double the size if we need to do compaction
+                    this._rQbufferSize *= 2;
+                } else {
+                    // otherwise, make sure we satisy rQlen - rQi + min_fit < rQbufferSize / 8
+                    this._rQbufferSize = (this._rQlen - this._rQi + min_fit) * 8;
+                }
+            }
+
+            // we don't want to grow unboundedly
+            if (this._rQbufferSize > MAX_RQ_GROW_SIZE) {
+                this._rQbufferSize = MAX_RQ_GROW_SIZE;
+                if (this._rQbufferSize - this._rQlen - this._rQi < min_fit) {
+                    throw new Exception("Receive Queue buffer exceeded " + MAX_RQ_GROW_SIZE + " bytes, and the new message could not fit");
+                }
+            }
+
+            if (resizeNeeded) {
+                var old_rQbuffer = this._rQ.buffer;
+                this._rQmax = this._rQbufferSize / 8;
+                this._rQ = new Uint8Array(this._rQbufferSize);
+                this._rQ.set(new Uint8Array(old_rQbuffer, this._rQi));
+            } else {
+                if (ENABLE_COPYWITHIN) {
+                    this._rQ.copyWithin(0, this._rQi);
+                } else {
+                    this._rQ.set(new Uint8Array(this._rQ.buffer, this._rQi));
+                }
+            }
+
+            this._rQlen = this._rQlen - this._rQi;
+            this._rQi = 0;
+        },
+
         _decode_message: function (data) {
             // push arraybuffer values onto the end
             var u8 = new Uint8Array(data);
+            if (u8.length > this._rQbufferSize - this._rQlen) {
+                this._expand_compact_rQ(u8.length);
+            }
             this._rQ.set(u8, this._rQlen);
             this._rQlen += u8.length;
         },
@@ -362,22 +403,7 @@ function Websock() {
                         this._rQlen = 0;
                         this._rQi = 0;
                     } else if (this._rQlen > this._rQmax) {
-                        if (this._rQlen - this._rQi > 0.5 * this._rQbufferSize) {
-                            var old_rQbuffer = this._rQ.buffer;
-                            this._rQbufferSize *= 2;
-                            this._rQmax = this._rQbufferSize / 8;
-                            this._rQ = new Uint8Array(this._rQbufferSize);
-                            this._rQ.set(new Uint8Array(old_rQbuffer, this._rQi));
-                        } else {
-                            if (ENABLE_COPYWITHIN) {
-                                this._rQ.copyWithin(0, this._rQi);
-                            } else {
-                                this._rQ.set(new Uint8Array(this._rQ.buffer, this._rQi));
-                            }
-                        }
-
-                        this._rQlen = this._rQlen - this._rQi;
-                        this._rQi = 0;
+                        this._expand_compact_rQ();
                     }
                 } else {
                     Util.Debug("Ignoring empty message");